Alkaline primary batteries and, in particular, alkaline manganese dioxide/zinc dry cells (MnO.sub.2 /Zn), have been a successful commercial development. When manufactured in a cylindrical configuration, the battery seal is typically made by compressing a plastic member (gasket) within a metal can by crimping the open end of the can as disclosed by Ralston and Ko in U.S. Pat. No. 3,663,301. More particularly, in the typical commercial alkaline primary batteries, the battery seal comprises the nickel plated steel can, i.e., the positive current collector, a plastic seal member, typically of nylon or polypropylene, and a sealant between the metal can and the plastic seal member. However, cells constructed according to the disclosure of Ralston and Ko are susceptible to electrolyte leakage. Such leakage usually occurs at the interface of the gasket and the metal can and is due to the propensity of alkaline electrolytes to wet metal surfaces.
To reduce the leakage of electrolyte from alkaline cells, sealant materials are used between the gasket and the metal surface. Typically asphaltic compounds such as bitumen are used. However, such seals are only marginally satisfactory, and then only when the steel cans are plated with nickel. When the steel can is unplated, such seals are very poor. The poorer seals noticed with unplated steel cans are probably due to differences in the bonding strength of bitumen to steel and bitumen to nickel-plated steel.
Others, attempting to improve upon the seals of alkaline batteries have used sealants consisting of fatty polyamides, e.g., U.S. Pat. No. 3,922,178 to Winger, cured epoxy-polyamine resins, e.g., U.S. Pat. No. 3,713,896 to Feldhake, or both bitumen and fatty polyamide resins, e.g., Japanese patent Application No. J5-4007-536. However, as explained in U.S. Pat. No. 4,282,293 to van Lier, all of these solutions have the same drawback--leakage still occurs since these materials do not always completely seal the interface of the metal surface and the gasket. It is hypothesized that leakage results from the inability of the sealant, or sealants, to adequately bond to the metal surface. Moreover, sealants such as bitumen and fatty polyamides are soft, somewhat tacky materials at and above room temperature and so are subject to damage and contamination during the assembly of electrochemical cells. Even cured epoxy-polyamine resins, though non-tacky, are relatively soft and can cause problems during cell assembly.
The battery seal set forth in U.S. Pat. No. 4,282,293 solves many of the processing problems as described above. However, as with cells incorporating bitumen and polyamides in the seal area, extreme care must be taken to confine the organosilane resin of the van Lier patent to the immediate area of the seal, otherwise the electrical operation of the cell will be adversely affected by the introduction of a non-conductive layer between the electrode and current collector.
It is a primary object of the present invention to provide for a stronger seal for alkaline cylindrical cells.
Another object of the present invention is to provide for strong seals in alkaline cylindrical cells wherein the metal cans, i.e., the positive current collectors, are unplated steel.
Still another object of the present invention is to provide for a strong seal in an alkaline cylindrical cell which is easy to make and is compatible with the alkaline cylindrical cell assembly process.
The foregoing and additional objects will become more fully apparent with the following description.